United States emergency departments (EDs) are a vital component of the health care system because they: (1) are the only site that provides 24-hour acute care; (2) are the most frequent access point for inpatient care; and (3) function as the health care safety net.1 ED care is critical for the acute management of almost every major cause of hospital admission and death in the United States, 2-4. Moreover, care provided in the ED has been shown to have a significant impact on mortality, 5-9 and once started in the ED, evidence-based care is more likely to be maintained during hospitalization,10. Despite the importance of quality of care provided in the ED, little is known about ED quality of care or barriers to quality of care in the ED. Acute coronary syndrome (ACS), acute ST elevation myocardial infarction (AMI), community-acquired pneumonia (CAP), acute ischemic stroke (AIS), and severe sepsis and septic shock (SS) are 5 ideal disease processes to study ED quality of care given that they are all common reasons for hospital admission,3 are associated with significant morbidity, mortality, and health care costs,2-3 are initially treated in the ED,3 nd all have ED based clinical practice guidelines (CPGs) that impact patient outcomes.54-58 We plan to study physician adherence to CPGs related to these 5 diseases in order to provide the first comprehensive and comparative study on ED quality of care and barriers to ED quality of care. The first hypothesis is that adherence to CPGs in the ED deviates from a criterion threshold defined a priori as 95% and adherence to CPGs in the ED varies between disease specific CPGs. The second hypothesis is that patient, provider, and environmental factors are significantly associated with poor adherence to ED CPGs. The Specific Aims therefore include: (1) to perform a multi-center retrospective study to estimate adherence deviation from a criterion threshold and adherence variation between disease specific CPGs among ED patients with ACS, AMI, CAP, AIS, and SS; (2) to perform a qualitative study to identify provider knowledge, attitudes, and perceived barriers to ED adherence of CPGs for ACS, AMI, CAP, AIS, and SS; and (3) to perform a multi-center retrospective study to estimate associations between patient, provider, and environmental factors and ED adherence of CPGs for ACS, AMI, CAP, AIS and SS.